Recent years have seen an accelerating trend in the commercial use of bio-resins across a wide range of products. This growth has been driven by a range of factors. With the petrochemical based polymers likely to be more limited and expensive in coming years, the availability of materials based on sustainable, renewable resources is a key factor. For disposable products such as packaging ease of disposal via a composting route is another important advantage over traditional materials.
One limitation with so-called bio-resins is the relatively low temperature performance of these materials. For instance polylactic acid (PLA) is a widely available biopolymer, but in its amorphous form it has a glass transition temperature (Tg) around 58° C., and softens and shows poor form retention above this temperature. Although the temperature performance can be improved by crystallizing the polymer, attempts to carry this out commercially have met with very limited success.
Another limitation is the processing performance of these materials. For example cellulose acetate is produced by reacting acetic anhydride with cellulose. The resulting polymer is quite rigid and shows good stiffness and strength, but is relatively difficult to process. It can be processed in solution (e.g. with acetone) or by adding plasticisers to soften the polymer and allow melt processing by e.g. injection moulding and sheet extrusion. Whilst such technologies are well known, the addition of too much plasticiser can reduce the mechanical properties of the final product, especially at higher temperatures, as well as reducing the glass transition temperature. On the other hand too little plasticiser leads to low melt flow and difficulties in processing.